On the most recent versions of Kindle Android app is fairly simple to change the standard dictionaries with custom ones. One simply has to go to Android -> Data -> com.amazon.kindle -> files, find the filename associated with a certain language and give it to the custom dictionary.

For instance, I want to replace the German standard dictionary that I never use for a custom ENG-POR dictionary: I simply rename it to B003YL4LVQ_EBOK.prc (German dict filename), copy it to the com.amazon.kindle folder replacing the existing file, delete the bookmark file (B003YL4LVQ_EBOK.embp), restart device and it is done. Hence, when I'm reading a book, I just need to click on the book icon on the definition window and change to German to have access to my ENG-POR dictionary

On Kindle 3.2.0.35, the one that works on Nook Touch, it's a little different and requires more steps:

- it is not possible to change dictionaries inside the app, you're stuck to the standard one of each language;

- the dictionaries files are on folder Kindle (main root), with the rest of the e-books;

- besides changing the filename to B003ODIZL6_EBOK.prc, it' is also needed to change ASIN and other metadata. For this I use mobimetaeditor.

So, I wanted to replace the standard ENG dictionary for a custom ENG-POR that I've purchased on Amazon. I've changed it's filename to B003ODIZL6_EBOK.prc and edited with mobimetaeditor the following metadata criteria to match the standard one. To simplify, I'll list what I've edited: